On Jan 15, 19:35, Max Eskin wrote: Pass. Actually, you can have 4, if you have a controller at the secordary floppy controller address as well as at the primaryfloppy controller address. Each controller can only have two drives because of a silly hardware setup chosen by IBM. On a normal SA400-style interface, there are 4 drive selects, and one of each other control signal; each control signal is normally gated (on the drive) with the approriate select line. IBM chose to use an arrangement where completely separate motor-on signals were provided for the two drives. The way they did this was to arrange the signals in the cable such that one drive used a particular drive select and the motor signal in the standard place, and the other drive used a different select with the moror signal on a different wire. Hence the infamous cable twist, such that each drive sees a particular drive select (it's the second select line) and the motor-on signal in the standard place. However, from the point of view of either drive, there is another motor signal on a pin which would otherwise be a select line for another drive. Thus you can't use all 4 drive selects, and hence only two drives per controller cable. Another way to look at it, is to assume that IBM wanted all drives to have the same jumper settings, including the drive select jumper. But instead of putting a twist in the cable which would just swap some of the select lines, they used a twist over a wider section. Unfortunately that also moves the motor control line to where a select line would normally be. Thus they need another motor control line somewhere else (where a drive select would be, obviously), and end up only being able to put half as many drives on the bus. -- Pete Peter Turnbull Dept. of Computer Science University of York